This invention relates to porous ceramic bodies having a contoured shape that is particularly suitable for use as a carrier for catalytically active material. The combination of carrier and active material may function as a catalyst when randomly disposed within a reactor tube which is useful in the manufacture of chemicals such as ethylene oxide.
Ethylene oxide, which may be abbreviated herein as EO, is an important industrial chemical used as a feedstock for making such chemicals as ethylene glycol, ethylene glycol ethers, alkanol amines and detergents. One method of manufacturing ethylene oxide is by the catalyzed partial oxidation of ethylene with oxygen. There are continuing efforts to develop catalysts that can improve the operating efficiency of such ethylene oxide manufacturing processes. Some of the desirable properties of an ethylene oxide catalyst include good selectivity, good activity, and long catalyst life. It is also important that the catalyst as loaded in the reactor tubes results in as relatively low pressure drop across the EO reactor as is possible. Achieving significant pressure, drop improvement with higher packing density would enhance the stability of an EO catalyst in existing EO plants and would allow for the design of more efficient new EO plants.
The typical catalysts employed to make EO comprise silver and other metals and promoters on a carrier, typically an alpha alumina carrier. These silver catalysts are described in many US and foreign patents, including, among others, U.S. Pat. Nos. 4,242,235; 4,740,493; 4,766,105; 7,507,844; 7,507,845; 7,560,577; 7,560,411; 7,714,152; US 2008/0081920; US 2008/0306289; US 2009/0131695 and US 2009/0198076. The shape of the catalyst takes the shape of the carrier. The shape of a carrier may be characterized by describing one or more of the following features: length, outer diameter, inner diameter; ratio of length to diameter; radius of an exterior wall; radius of an end surface; shape when viewed from an end; and shape when viewed from a side. The most common commercially available carrier shape is a small cylinder pellet shape with a hole in the center of the pellet. See, e.g., U.S. Pat. No. 7,259,129, which disclosure is herein incorporated by reference. In the '129 patent the support material has specific physical properties and is preferably formed into a shaped agglomerate of the support material having a hollow cylinder geometric configuration or structure with a relatively small internal diameter. In contrast, U.S. Pat. No. 4,441,990 discloses hollow shaped catalytic extrudates which may be employed in catalytically promoted processes including hydrocarbon processing operations. The shapes include essentially rectangular shaped tubes, and triangular shaped tubes in cross section. One embodiment is characterized by having bulbous protrusions around the external periphery. Wall thicknesses from about ⅛ inch, 1/10 inch, or even 1/25 inch or less are disclosed. US 2009/0227820 discloses a geometrically shaped refractory solid carrier in which at least one wall thickness of the carrier is less than 2.5 mm. U.S. Pat. No. 6,518,220 discloses shaped catalysts for heterogeneously catalyzed reactions in the form of hollow cylinders or annular tablets whose end faces are rounded both to the outer edge and to the edge of the central hole, so that they have no right-angled edges. One modification of such a catalyst shape comprises a pellet where the rounded edges are only on the outer edge of the pellet, and the inner edge of the central hole does not comprise rounded edges. U.S. Pat. No. 6,325,919 discloses catalyst carriers composed of a refractory inorganic oxide having a rotationally symmetrical shape having a hollow portion, such as a doughnut shape. An outer peripheral surface and the inner peripheral surface separating the hollow portion are linked by curved surfaces, and the height of the carrier along the rotational symmetry axis is less than the outer diameter of the carrier. EP 1,184,077 discloses a porous refractory carrier in the form of an angular extrudate with rounded edges. WO 03/013725 discloses elongated shaped trilobal particles. U.S. Pat. No. 2,408,164 discloses numerous shaped catalyst including planar, cylindrical with a central opening and a plurality of parallel grooves disposed in the outer periphery, and cylindrical with several parallel passageways formed therein. U.S. Pat. No. 4,645,754 discloses catalysts made from a carrier that is in the shape of Intalox saddles or Berl saddles. Other shapes that have been mentioned in the patent art include spheres, tablets, rings, spirals, pyramids, cylinders, prisms, cuboids, cubes, etc. See, for example: US Published Patent Applications 2008/0015393, 2008/0255374, 2009/0041751, 2009/0227820; U.S. Pat. Nos. 5,155,242 and 7,547,795; and international publication WO 2004/014549.
However, there continues to be a need for improved catalysts having better performance in the reactor than currently are available. The present invention provides carriers and catalysts that enable such an improvement.